Interesting cards. Some comments

They Do Not Die
First action should be response, not skirmish. And the limit is worded unclearly. I guess you want to make it impossible to stack multiple minions here. So it should be worded like
Flung Into the Fray.
Response: If no minion is stacked here and your twilight minion is about to be killed in a skirmish, stack that minion here.
Hidden to All But Him
Do you want it to work also when the Ring-bearer puts on The One Ring during a fierce skirmish (and losing fierce doesn't hurt at all as fierce assignments are already done)? If not, add "Cancel all fierce skirmishes involving a Nazgul." to the card. But maybe it's not needed, card may be not overpowered as it is. This needs playtesting.
Morgul Invasion Force
Would sound better this way: If the fellowship is at a battleground site, exert this minion to add two threats. Also the phase where you can use this action is missing. I think it should be regroup (and definitely by no means skirmish), so that combo with
Morgul Destroyer isn't too good.
Panic
This also needs playtesting, but this may need to be made unique. Or at least get "Limit 1 per character" like
Blade Tip.
Poisoned Arrows
This card has completely no cultural enforcement. Maybe "Spot 5 archers and a
![Wraith [Wraith]](https://lotrtcgdb.com/forums/Smileys/classic/wraith.png)
Orc", or "Spot 5 archers and 2
![Wraith [Wraith]](https://lotrtcgdb.com/forums/Smileys/classic/wraith.png)
cards"? Events (that can never be spotted so no multiculture hate can be fueled by them) IMO should always have some cultural enforcement.
Gimli, Orc Killer
As you don't use resistance, I think he should have a signet. Each pre-Shadows Gimli (except the Ring-bearer one) had a signet.
Company of Rangers
It should be "spot 3
![Gondor [Gondor]](https://lotrtcgdb.com/forums/Smileys/classic/gondor.png)
companions", not "spot 3 Gondor companions".
Nazgul: interesting theme, would definitely be worth trying in a deck. You may think about moving abilities a bit between them a bit, so that Enquea gets one of the better ones, to make it a
hard choice between this, enduring, twilight and shotgun ones. I don't know if combining those Nazgul with
Morgul Brute,
It Wants to be Found and
Gollum, DaD won't be too powerful corruption, especially with
The One Ring, Ring of Rings not allowed.
And one more thing about using uppercase: on LotR cards, after a phase name, the following text starts with uppercase. For example "Skirmish: Exert this minion to add
![2 [2]](https://lotrtcgdb.com/forums/Smileys/classic/2.png)
", not "Skirmish: exert this minion to add
![2 [2]](https://lotrtcgdb.com/forums/Smileys/classic/2.png)
"